Or,it´s like sundial, the first turn without playing cards is yours.
You can only play Silence, if it is the FIRST card of the turn you play. You play the card, you can´t play other cards, your opponent can´t play cards, and you are able to play another Silence in the next turn..
This also prevents using this card in the 1st turn. (you always play quanta sources before you play a spell).